Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $83.31   11.320%   $92.7407   $92.74   $92.75   $92.70  
  Purchase #2 $89.38   9.358%   $97.7442   $97.74   $97.75   $97.70  
  Purchase #3 $185.58   3.517%   $192.1068   $192.11   $192.10   $192.10  
  Purchase #4 $109.81   3.725%   $113.9004   $113.90   $113.90   $113.90  
  Purchase #5 $221.74   11.766%   $247.8299   $247.83   $247.85   $247.80  
  Purchase #6 $102.35   8.367%   $110.9136   $110.91   $110.90   $110.90  
  Purchase #7 $151.55   6.486%   $161.3795   $161.38   $161.40   $161.40  
  7 purchase totals = $943.72       $1,016.6151   $1,016.61   $1,016.65   $1,016.50